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To determine the optimal light intensity and enable plants to cope with various environmental stresses in plant factories, the morphological and photosynthetic characteristics of ginseng seedlings, including the secondary metabolites, were investigated under six light intensities: 25, 50, 75, 100, 125, and 150 μmol m−2s−1. The shoot length increased with lower light intensity up to 75 μmol m−2s−1, and the leaf area and specific leaf weight were greatest at 100 and 75 μmol m−2s−1, respectively. Stomata frequency was higher from 100 μmol m−2s−1with higher light intensity, and single stomatal pore length also increased at 150 μmol m−2s−1. Net photosynthetic rate at light saturation and net photosynthetic rate in growth condition increased sequentially up to 100 μmol m−2s−1before rapidly decreasing at 150 μmol m−2s−1. The dark respiration rate and light compensation point were significantly high at 150 μmol m−2s−1only. Fv/Fm and chlorophyll content statistically differed from 63 and 84 days after seedling stand, respectively. Thus, the leaves withered to death with higher light intensity. The ginsenoside content in the roots significantly increased according to the light intensity, and the panaxadiol/panaxatriol (PT) ratio tended to decrease as the PT-type ginsenosides increased further. Taken together, the range of 75–100 μmol m−2s−1was found to be beneficial for growth, photosynthetic acclimation response, and total accumulated ginsenosides of ginseng seedlings.

Ginseng, a semi-shade perennial plant, is greatly affected by light. However, light quality has only been studied in a few papers involving growth tests under monochromatic light or based on hairy root cultures. A plant factory with light-emitting diodes (LEDs) may provide high precision and standardization of ginseng seedlings for transplanting, and plant responses to light quality should be investigated for designing the optimal lighting conditions for this environment. In this study, various ratios of red light (R):blue light (B) were set from 100:0 to 0:100% at the same photosynthetic photon flux density of 75 μmol m−2s−1. As R increased, the shoot length became longer from R75B25, resulting in the single treatment of R being 1.68 times that of B. Compared to monochromatic R or B treatments, the overall growth of ginseng seedlings in R50B50 treatment increased. In the mesophyll structure, mixed light as R50B50 or while LEDs increased starch grains, and only R treatment led to dense chloroplasts in palisade and spongy parenchyma cells. Increasing R ratios had negative effects on CO2assimilation rate (AN), light-saturated net photosynthesis rate (Asat), and chlorophyll parameters. The higher the R ratio, the higher the ginsenoside content in leaves, while roots were less affected by spectral changes. Monochromatic R induced malformation and senescence of ginseng leaves, while the addition of 25% B was sufficient to prevent the abnormal development of leaves and dysfunctional photosynthetic operation of ginseng seedlings. The results suggest that combinations of R and B should be considered when designing artificial lighting systems for a closed-type plant factory since R affects the morphological characteristics and ginsenoside content of ginseng seedlings.